LONDON—Scotland’s main pro-independence party is unlikely to win an outright majority in Thursday’s parliamentary election, a blow to its hopes of demanding a referendum on separating from the United Kingdom, a Savanta Comres/The Scotsman poll indicated. The Scottish National Party (SNP) wants a majority in the devolved parliament to demand another referendum, although British Prime Minister Boris Johnson has repeatedly said he will not grant one. The Savanta Comres/The Scotsman poll indicated that the SNP would fall six seats short of winning an outright majority but that the Green Party, which cooperates with the SNP, could win as many as nine seats. “If these polling figures play out on Thursday’s vote it’ll likely leave the SNP short of the majority,” said Chris Hopkins, political research director at Savanta ComRes. The Greens in Scotland, which have cooperated with the SNP to pass legislation, are pro-independence and have not ruled out a …